Kernel/LibC: add dup() syscall and function

kernel/include/kernel/OpenFileDescriptorSet.h

@@ -25,6 +25,7 @@ namespace Kernel
 
 		BAN::ErrorOr<void> pipe(int fds[2]);
 
+		BAN::ErrorOr<int> dup(int);
 		BAN::ErrorOr<int> dup2(int, int);
 
 		BAN::ErrorOr<void> seek(int fd, off_t offset, int whence);

kernel/include/kernel/Process.h

@@ -86,6 +86,7 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_creat(BAN::StringView name, mode_t);
 
 		BAN::ErrorOr<long> sys_pipe(int fildes[2]);
+		BAN::ErrorOr<long> sys_dup(int fildes);
 		BAN::ErrorOr<long> sys_dup2(int fildes, int fildes2);
 
 		BAN::ErrorOr<long> sys_seek(int fd, off_t offset, int whence);